Many processes for forming fused ceramic bodies begin by forming porous green bodies, which are composed of a batch material that includes particulates of inorganic compounds held together with binders. One of the final steps in these processes is a firing step in which the original particulates are reacted to become a fused ceramic body. Often all or most of the binders burn out in this firing step. These processes have constraints, including green bodies with large particulates and large pores (e.g., greater than 10 microns average size), that experience high sag in firing due to a low ratio of sintering forces relative to gravity forces. Green bodies that have high porosity can have very low strength in firing and will often fracture or crumble before particles fuse.
One approach taken to address the above constraints is adding one or more high temperature binders to the material mixture of the body prior to forming the body. An organometallic pre-ceramic precursor binder can be added to the batch material, which is formed into the green pre-formed bodies. The ceramic precursor binders contribute to the overall ceramic content of the finished part. In another approach, a pre-formed green body can be heated to burn out traditional binder and then infiltrated with a pre-ceramic organic or inorganic binder material that can be a monomer, oligomer or polymer in a solvent. This binder can include an organometallic material.
Sol gel materials have been made, for example, using metal alkoxides or metal salts, organic solvents and acid or base catalysts. While much interest in these materials was generated when they were first developed decades ago, glass or crystalline bodies formed using sol gel materials were expensive and difficult to process. For example, the drying step used to prepare monolithic fused glass bodies was carried out by very slow drying or expensive supercritical drying. As a result of the difficulties of using sol gels to form large monolithic bodies, sol gel technology has been applied to areas including thin films and fiber coating. For example, ceramic matrix composites can be made by infiltrating fiber performs with ceramic sols to form a ceramic matrix material.